CURRENT LITERATURE. 181 



Hepaticae 



Evans Alexander W- A Taxonomic Study of Dumortiera 

 Bulletin of the Torrey Botanical Club, Vol. 46, No. 5, {May 1919). 



The writer gives a historical account of the genus, and fully examines 

 critically the various characters which have been used by various writers on 

 this genus. Stephani recognised three species in his species Hepaticarum in 

 1899 and Campbell published last year the description of a fourth species. 

 The writer however recognises only two species on the basis of the char- 

 acters drawn from the structural features of the vegetative thallus, and says 

 that the characters "drawn from the size and method of branching of the 

 thalus seem especially unreliable, Those drawn from the female receptacle 

 and the spores are scarcely more satisfactory." The writer has examined a 

 very large number of specimens and gives a full list of synonyms and the 

 places from which the plants came. The following is the key which he 

 gives : — 



Upper surface of the thallus smooth or nearly so throughout (although 

 often showing vestigial air chambers) D. hirsuta. 



Upper surface of the thallus with crowded papilliform cells, at least in 

 certain portions (always showing vestigial air chambers). D. nepalensis. 



S. R. K. 



Allen, E. R., Soma Conditions Affecting the Growth of Azotobac- 

 ter chroococcum. Annals of the Missouri Botanical Garden, Vol. VI. 

 No. l,p.I (Feb. 1919). 



The Nitrogen-fixing bacterium Azotobacter has since its discovery by 

 Beijerinck in 1901 been the subject of considerable study; and it has been 

 found by many workers that growth in ordinary synthetic culture media is 

 poor, but that an aqueous extract of soil or even tap — instead of distilled 

 water causes a marked improvement. Kzyemieniewski, in 1908, found that 

 the humus was the important constituent of soil, and several suggestions as 

 to the meaning of this have been made. One is that the beneficial result is due 

 to the presence of iron and aluminium-silico-phosphates, but as the optimum 

 quantity of the former lies at 10 mg per 100 cc, and is thus considerably 

 above that which would be required for nutrition, H. Fischer suggested that 

 the role of humus or of the Fe 2 3 is that of an oxygen carrier. Bottomly 

 in 1914 suggested that certain bodies, analagous to vitamines and which he 

 called • auximones ', are liberated from peat treated with certain anoerobic 

 bacteria, and that there auximones are the cause of the action of humus in 

 cultures of Azotobacter. In the paper under notice the author describes 

 experiments which point to the need of phosphorus and the absence of all 

 acid in the culture-medium as the chief requirements, and that it is unneces- 

 sary to postulate the action of colloidal oxygen carriers or of any special and 

 rare or supposed constituents or products of the soil-humus such as 



anximones. 



P. F. F. 



Printed and Published for the Proprietor by W. L. King at the Methodist 

 Publishing House, Mount Road, Madras. 



